The revolving door is based on a simple idea. By replacing conventional
swinging doors with four equally spaced doors that rotate around a central
pivot, revolving doors are never open to both the outside and the interior
of a building at the same time. If you have ever sat near the door
of a restaurant or another nice warm space on a cold day (and who hasn't?),
you know how cold air rushes in every time the door swings open.
If it is not only cold, but windy besides, the cold blasts can be even
worse.

Revolving doors are expensive and relatively few restaurants have them.
They are common, however, in skyscrapers, where they serve several important
purposes. Their major function in a skyscraper has to do with equalization
of air pressure. When a tall building is heated, the hot air rises, reducing
the air pressure at ground level and on the lower floors. Swinging
doors in such buildings allow higher-pressure cold air to enter, creating
their own wind and blowing around papers, hats, and anything else that
is not tied down. Revolving doors not only make the lobbies of these
buildings more pleasant, they reduce energy costs by preventing cold air
from entering.

Revolving doors also serve an important architectural purpose.
According to Andrew S. Dolkart, an architectural historian at Columbia
University, "Architects carefully choreograph a building's entrance. Every
element is designed to create a sense of vastness," he noted. In
an article in The New York Times last year, Dolkart cited the Chrysler
Building as an example of the skillful use of revolving doors.
The exterior of the building suggests that it will have a towering lobby,
but in fact the lobby's ceiling is relatively low. "When you walk
from the small space in the revolving door and step into the lobby the
space just seems to explode. The lobby feels so big compared to the
small space in the door that you don't even notice that the lobby isn't
as big as you thought it would be. That small space in the door is
critical to creating the illusion."

Although New York City, with its profusion of skyscrapers, is generally
regarded as the revolving door capital of the world, the revolving door
was actually invented in Philadelphia by Theophilus
Van Kannel, who patented the device in 1888. Van Kannel, who
was recognized for his invention with an award from the Franklin Institute,
founded the Van Kannel Revolving Door Company, which eventually was bought
out by the International Steel Company.

In today's security-conscious environment, revolving doors also have
another advantage: they can make it easier to control access to a
building. As can been seen in one of the links below, revolving doors
can be outfitted with biometric devices, metal detectors, and other screening
and access control mechanisms.

Finally, although it probably was not what Theophilus Van Kannel had
in mind, going around and around in a revolving door can be lots of fun--especially
if you're a kid.

Links:

The International Revolving
Door Association. First on its list of objectives is "to contribute
and direct the development of international safety standards through interaction
with various local and global regulatory authorities." Under Q&A,
the site provides brief information on safety, security, energy use, and
other subjects. There is also a rather nice gallery (source of the
photo above).

International
Revolving Doors of Evansville, Indiana, a direct corporate descendant
of the Van Kannel Company described above, has an extensive web site with
information on the history and advantages of the revolving door in addition
to descriptions of its products.

"Why Install
a Revolving Door?" The AGP Group, an Australian firm has the
answer: it keeps the wind out. The company offers a wide range of
revolving doors, from budget to high end.

Crane Revolving Door Company
of Lake Bluff, Illinois, describes itself as "the leader in high-end revolving
doors." Its site features a photo gallery of its installations.

Safesec Corporation
of Ontario, California, sells security-oriented revolving doors.
Described as "entrance control solutions," its products offer such options
as biometric devices and metal detectors. Quintron
Systems, Inc., has a similar product line. And ABACOS
Automation of Lanarkshire, U.K., makes revolving doors with bulletproof
glass.

Boon Edam BV of the Netherlands describes itself (in a 2008 e-mail to me) as the
"acknowledged world market leader in revolving doors." It lists among its accomplishments "the
world's first energy generating revolving door."

The Half-Bakery, a site that collects some strange ideas for inventions,
features a "revolving
doors clock." It would have three doors, one making a full rotation
in 12 hours (with an entrance-exit time of six hours), one rotating in
an hour, and the third in one minute. It seems unlikely to catch
on.